Method of producing a suitable product for nitriding and alloying steel



3,350,242 METHOD OF PRODUCING A SUITABLE PRODUCT FOR NITRIDING AND ALLOYING STEEL Alfons Fuchs, Buderich, near Dusseldorf, Germany, as-

signor to Gesellschaft fiir Elektrometallurgie m.b.H., Dusseldorf, Germany No Drawing. Filed Aug. 17, 1965, Ser. No. 480,481 Claims priority, application Germany, Aug. 20, 1964,

G 41,360 9 Claims. (Cl. 148-16.6)

Theinvention relates to a method of producing a product suitable for nitriding and simultaneously alloying steel.

As known the technological properties of steel can be improved by the introduction of contents of nitrogen in the order of 0.010 to 0.02%. This applies both to unalloyed and to alloyed steels which unavoidably already contain 0.002 to 0.005% nitrogen when produced by conventional metallurgical processes.

In order to achieve the desired higher nitrogen content, for instance, steel fining alloys with a higher nitrogen content may be added to the steel. Such steel fining alloys include ferromanganese, ferrochrome, ferrotitanium, ferrovanadium as well as manganese vanadium alloys and others. Nitriding ferro-alloys of this kind are rather expensive and their nitrogen content is relatively low. Consequently a fairly large quantity of such alloys must be added to provide the desired nitrogen content in the steel.

At the same time their introduction often involves the simultaneous presence of undesirably high contents of metal alloying elements in the steel.

In order to over-come this difficulty it has beefi proposed to use lime-nitrogen (calcium cyanamide CaCN for introducing the necessary nitrogen into the steel.

Calcium cyanamide has a substantially higher nitrogen content than steel fining alloys. It is about 20 to 24%, and lime nitrogen is much more inexpensive to produce than the nitrided ferro-alloys. However, lime nitrogen which is used as an addition to the tap ladle has decisive drawbacks. It must be carefully pre-treated to remove hydrate and moisture, since otherwise the steel may take up hydrogen. The alloying of lime nitrogen must also be carefully done to prevent moisture from being picked up and the same damage resulting as when using a product that has not been properly dried. Lime nitrogen is finegrained or a powder and therefore tends to be blown away when it is introduced to the steel, causing losses of nitrogen besides being a nuisance to personnel. Owing to its low specific gravity difficulties also arise in mixing the same with the steel. When producing low alloyed steels the separate addition of steel fining alloys is also required.

It is the object of the present invention to provide a method whereby a product can be obtained that does not share the drawbacks of knownsubstances for nitriding steel.

More particularly it is proposed to provide a simple method which Will lead to a product of relatively high specific gravity.

The invention solves the contemplated problem by mixing calcium carbide with one or more steel fining alloys and by nitriding the same in a nitrogen atmosphere, a process which leads to a sinter product. It is best to add to the ground calcium carbide, size-reduced steel fining alloys in quantities up t 40% and then to perform the nitriding and sintering operation in a nitrogen atmosphere.

nited States Patent 0 Generally speaking, a quantity under 10% would not be used. In order to facilitate the nitriding process and to reduce the reaction temperature, 1 to 3 fluorspar may be added to the mixture of calcium carbide and steel fining alloys. It has been found useful also to add 2 to 7% of lime nitrogen to this mixture because it assists the reaction during the nitriding and sintering process.

The proposed method provides a sinter product resembling lime nitrogen, but the sinter product also contains a major or minor quantity of one or more steel fining elements, such as manganese, chromium, vanadium, titanium or the like. Consequently, the product is substantially heavier than normal lime nitrogen and it is therefore easier to introduce into the steel, particularly since it becomes available in lumpy form. Special care during the alloying process is not necessary and there is no evolution of dust when adding it to the steel.

Production can be performed in a particularly simple way. The mixture of calcium carbide and steel fining alloys is filled into suitable metal containers and these are placed into furnaces for the production of lime nitrogen. By utilising the heat generated during the formation of lime nitrogen the mixture is heated up to reaction temperature and nitrided and sintered in this way.

However, it must be borne in mind that the steel fining alloys, such as the ferromanganese, ferrochrome, ferrovanadium, ferrotitanium, manganese-vanadium and so forth must be appropriately size-reduced to a grain size which does not exceed 0.3 mm. 0.15 mm. has been found a useful size of grain.

Nitriding of the carbide-steel fining mixture proceeds without adversely affecting the simultaneous production of lime nitrogen and the excess heat generated in this latter reaction is utilised. The nitriding process and sintering of the carbide steel fining mixture proceeds practically at the same temperature and within the same period of time as the normal production oflime nitrogen. The container in which the mixture is reacted and sintered must be inserted into the container in which the lime nitrogen is produced to ensure that the desired temperature will be reached.

The described method can be most conveniently performed in lime nitrogen plant operating on the basis of the known Polzeniusz or Frank Caro process (Ullmann, Encyklopaedie der technischen Chemie, vol. 5, 1954,

The sinter product which becomes available in plate or block shape is broken down to a grain size that can be handled with shovels, packed in sheet iron drums or barrels and despatched to the steel works. The addition to the steel is manually done with a shovel without molestation of personnel by the evolution of dust or the like.

The specifically heavy sinter product more readily sinks in the steel than a normal linenitrogen, it rapidly dissolves and thus ensures a uniform distribution in the steel ofboth the nitrogen and the alloying elements con-.

scribed. The primary substances mentioned in the examples had the following compositions or contents.

EXAMPLE 1 A starting mixture weighing 49 kg. and containing a ferromanganese with a low carbon content had the following composition;

Kilograms Ferromanganese 11 Calcium carbide 35.5 Fluorspar 0.7 Lime nitrogen 1.8

From this there were produced 65.5 kg. of a sinter product containing:

Percent Nitrogen 18.3 Manganese 13.3 Iron 3.1

EXAMPLE 2 A starting mixture weighing 113 kg. containing a ferromanganese with a low carbon content had the following composition:

Kilograms Ferromanganese 34 Calcium carbide 74 Fluorspar 2 Lime nitrogen 3 From this mixture 151 kg. of a sinter product Were obtained containing:

Percent Nitrogen 17.1 Manganese 16.3 Iron 3.8

EXAMPLE 3 The composition of a total initial charge of 50 kg. containing ferromanganese with a high carbon content was as follows:

Kilograms Ferromanganese 17.4 Calcium carbide 31.0 Fluorspar 0.6 Lime nitrogen 0.9

4. This provided 59.8 kg. of a sinter product containing: Percent Nitrogen 16.7 Manganese 21.0 Iron 5.6

In these examples the stated contents of the sinter product are those which are of interest for use of the product in a steel works. However, the entire analysis of the sinter product according to Example 3 that can be produced according to the invention may be hereunder noted:

Percent Manganese 21 Nitrogen 16.7 Iron 5.6 Carbon 17.5 Calcium about 34.0 Silicon about 0.5 Aluminum about 0.8 Magnesium about 0.2 Chromium, nickel, titanium, copper and vanadium taken together less than 0.2

The major proportion of the nitrogen content of the product is in the form of calcium cyanamide and the minor portion is in the form of manganese nitride. The carbon content is present in the carbide as calcium cyanamide as Well as in the form of free unbound carbon. The calcium is contained in the calcium cyanamide and bound with oxygen in the form of lime.

What I claim is:

1. A method of producing a product for nitriding and alloying steel, which comprises nitriding and sintering in a nitrogen atmosphere a mixture comprising calcium carbide and at least one steel-fining alloy.

2. A method of producing a product for use in nitriding and alloying steel, which comprises nitriding and sintering in a nitrogen atmosphere a mixture of discrete material comprising calcium carbide and at least one ferro-alloy.

3. A method of producing a product for nitriding and alloying steel, which comprises nitriding and sintering in a nitrogen atmosphere a mixture comprising ground calcium carbide and comminuted steel-fining alloy in quantity up to 40% of the mixture.

4. The method according to claim 1, which comprises the step of incorporating from 1 to 3% fluorspar and from 2 to 7% of calcium cyanamide in the mixture.

5. The method according to claim 1 in which the steelfining alloy material in the mixture is of a grain size not exceeding 0.3 mm.

6. The method according to claim 5 in which the steelfining alloy material in the mixture is of a grain size of approximately 1.5 mm.

7. The method according to claim 2 in which the ferroalloy is ferromanganese.

8. The method according to claim 1, wherein the said mixture contained in a suitable container introduced into a furnace used for the production of lime nitrogen is heated in a nitrogen atmosphere prevailing therein, utilising the heat generated in this process, and sintered.

9. The method according to claim 1 comprising the step of comminuting the sintered product.

No references cited.

DAVID L. RECK, Primary Examiner. W. W. STALLARD, Assistant Examiner. 

1. A METHOD OF PRODUCING A PRODUCT FOR NITRIDING AND ALLOYING STEEL, WHICH COMPRISES NITRIDING AND SINTERING IN A NITROGEN ATMOSPHERE A MIXTURE COMPRISING CALCIUM CARBIDE AND AT LEAST ONE STEEL-FINING ALLOY. 